In the process of manufacturing various products such as paper and cardboard, pulp is produced as an intermediate product. The pulp is produced from wood chips which are sized and screened for removal of unwanted materials and then fed into a digester apparatus. In the digester apparatus, the temperature and pressure are raised to levels in the order of 300.degree. F. and 150 psig, causing the lignin in the wood to be removed. The remaining product, which is called pulp, is a generally brown or greyish slurry which has the general consistency of wet tissue paper. The pulp is removed from the digester by pressure pumps which transport the pulp from the digester to a storage tank.
The consistency and strength of the fibers in the newly manufactured pulp is an important factor in determining the quality of the finished paper or cardboard product and a means for extracting a representative sample of the pulp is required in order to perform the appropriate quality control tests.
In the past, various types of apparatus have been used in an attempt to remove representative samples of the pulp as it is transferred from the digester. The most common technique for pulp sampling includes the use of a valve which is attached to the conveying line. The valve is opened allowing some of the pulp in the conveying line to flow through the valve into a suitable container. This technique results in numerous operational problems, most of which are due to the plugging of the valve and the ports due to the high concentration of fibers and other materials in the pulp.
Another technique for pulp sampling is called the "block and bleed" system. In this technique, the pulp is allowed to flow into a by-pass pipe line which is blocked by a strainer. The fiberous material in the pulp is strained and the liquid is allowed to continue on and rejoin the flow in the conveying system. The system is operated by a series of valves which are opened and closed in order to extract a pulp sample.
This system, like the previous system, must be operated manually, resulting in high operation costs and high maintenance costs. These systems also must be operated under conditions of high temperature and high pressure resulting in safety problems associated with manual operation.
The prior art related to sampling devices includes U.S. Pat. No. 3,383,924 issued to Ray R. Cordell, which includes a retractable sampling tube and an auger mounted in the sampling tube for cleanout of the sampling tube after each sampling operation. This device is particularly adapted for the sampling of finely granulated materials in pressurized conveyor lines, however it is not suitable for the sampling of slurries such as paper pulp which includes large particles of bark or other solid materials.